1. Field of the Invention
The present invention relates to copiers having automatic document feeders which produce copies of multi-sheet documents.
2. Description of the Prior Art
High-speed copiers having automatic feeders are currently in use to produce copies. In one example, a recirculating feeder is coupled to a copier and causes the copier to make collated copies of a multi-sheet document. The recirculating feeder automatically feeds individual sheets in succession from the bottom of a document stack (a multi-sheet document in the feeder tray) to the exposure platen for copying and returns such sheet to the top of the document stack while maintaining the original orientation. After each sheet of a document stack has been fed once, the document stack can either be fed again or removed from the feeder. Since the copy sheets are delivered from the copier in the same order as the original document sheets, collation of the copy sheets by a sorter accessory is unnecessary.
Occasionally, a sheet of the document stack will have a contrast or density which when copied by the copier at its normal copy setting will produce a poor copy. The term contrast, as used herein, refers to the rate of change (or slope) of the copy reflective density (Dout) with respect to the original document reflective density (Din). In this case, the practice is to remove this document sheet from the document stack and copy it individually, making a good intermediate or master copy. The master copy is then returned to the appropriate position in the document stack and copying undertaken. A problem with this technique is that when the master copy is copied, (making a copy of a copy), image quality may be unavoidably degraded.
Another contrast and density control technique is set forth in commonly assigned U.S. patent application No. 137,149, entitled Copy Contrast and Density Control, filed Apr. 4, 1980 now U.S. Pat. No. 4,350,435 to Fiske et al and now U.S. Pat. No. 4,350,435. The disclosed apparatus adjusts copier process parameters to produce copies having improved copy contrast and density. A memory has a stored matrix array of sets of copier process parameter information, with each set having values which correspond to specific levels of Vo, Eo, and V.sub.B respectively. The operator designates a particular set. Means responsive to the values of the designated set change the exposure E produced by exposure lamps, the voltage Vo initially applied onto the surface of a photoconductor by a charger and the bias V.sub.B applied to an electrode of a development station to provide a copy having improved contrast and density.
In U.S. Pat. No. 4,294,536 to Paxton, apparatus is disclosed in which contrast and density of copies of selected document sheets of a multi-sheet document are adjusted during production runs without making master copies. Paxton discloses two techniques. In the first, before a production run, an operator manually enters into memory the copier process parameter information for controlling copying of a particular document sheet. In another disclosed technique, in order to enter this information into memory, a multi-sheet document is inserted into a recirculating feeder. Each document sheet is fed to the exposure platen and at least one copy is made of it. If the copy is satisfactory, the document sheet is returned to the tray. If not, copies are made until a proof copy with the acceptable contrast and density is made. Copier process parameter information for the proof copy as well as the sequential position of this document sheet in the multi-sheet document are then entered into memory and the document sheet returned to the stack. After this process is completed, the recirculating feeder is operated and copies are made. For each document sheet for which a proof copy was made, a copy in accordance with stored copier process parameter information is made with contrast and density as exhibited by the proof copy so that when the entire multi-sheet document is copied, all the copies have desired contrast and density.
Although the Paxton techniques represent a significant advance in the art, there remain opportunities for improvement. In the first technique, an operator must properly identify the page number of the document sheet before its process information is entered into memory. If he makes a mistake, this copier process information may be applied to the wrong sheet of the document. In the second technique, at least one copy must be made of each document sheet before a production run can be undertaken which adds time and expense.